1. Field of the Invention
The present invention relates to a capacitance type displacement detection apparatus and a method of manufacturing the same, in particular, relates to the structure of a detection portion and a signal processing portion thereof.
2. Description of the Related Art
The capacitance type displacement detection apparatus (hereinafter called a capacitance, type sensor) is arranged in a manner that a transmission electrode and a reception electrode are formed on each of two scales provided so as to be able to move relatively to each other. The detection electrode detects that a magnitude of capacitive coupling between the transmission electrode and the reception electrode changes in accordance with the movement of the scale.
FIG. 4 shows the arrangement of the electrode portions of the capacitance type sensor. A transmission electrode 101a and detection electrodes 101b are formed on a scale 101 of two scales, while a reception electrode is formed on the other scale 102. The scale 102 on which the reception electrode is formed moves in the directions shown by arrows in the figure and the displacement of this scale is detected by the scale 101. The transmission electrode 101a is formed by arranging a plurality of electrodes. Every predetermined numbers of the plurality of electrodes are coupled commonly. At least three kinds, preferably, eight or more kinds of alternating signals which phases differ by a predetermined phase angle from one another are supplied to the respective commonly coupled portions. When the scale 102 displaces with respect to the scale 101, the reception electrode generates a composite signal in accordance with the displacement and the detection electrode 101b detects the composite signal. The two detection electrodes 101b are provided so as to sandwich the transmission electrode 101a and output two detection signals which phases differ by 180 degrees to each other. Noise contained in the detection signals can be removed by calculating and using a difference between these detection signals. The detections signals of the two detection electrodes 101b are in a differential relationship, so that an amount and the direction of the displacement of the scale 102 relative to the scale 101 can be detected by processing the detection signals in a signal processing portion. FIG. 5 shows the entire configuration of the capacitance type sensor. The aforesaid scale 101 is provided within a senor portion (detection portion) 110. The sensor portion 110 is formed by the patterning process on a glass or ceramic board. On the other hand, the signal processing portion is configured as a peripheral circuit board 112. The signal processing portion supplies, for example, the eight kinds of alternating signals to the transmission electrode 101a and receives and processes the detection signal from the detection electrodes 101b. The peripheral circuit board 112 includes a detection IC 112a and a peripheral circuit 112b including a capacitor and a resistor etc. on a plastic board made of epoxy resin etc. The sensor portion 110 and the peripheral circuit board 112 (the signal processing portion) are connected through a flexible printed circuit (FPC) 114.
In this manner, in the capacitance type sensor of related art, the sensor portion 110 is configured separately from the peripheral circuit board 112, and the wirings (for example, eight wirings for the transmission side and four wirings for the reception side) are drawn so as to transmit and receive the signals there between. Thus, the longer the drawing distance of the wirings is from the sensor portion to the detection IC 112a, the more likely noise mixes into the detection signal, so that there arises a problem that the detection error arises. In particular, since the signal intensity decreases in accordance with the miniaturization of the sensor portion 110, the influence of the noise on the detection signal becomes larger relatively in accordance with the miniaturization. Accordingly, there arises a problem that the detection accuracy is degraded.
Further, in the related art technique, since the peripheral circuit board 112 serving as the signal processing portion was configured by a resin board made of epoxy resin etc., there arises a problem that it is difficult to further miniaturize the peripheral circuit board due to the restriction of the design rule.
Accordingly, the invention has been made in view of the aforesaid problems of the related art technique. An object of the invention is to provide a capacitance type displacement detection apparatus and a method of manufacturing thereof which can suppress the mixing of noise by shortening the drawing length of wirings between a detection portion and a signal processing portion and miniaturize the entire size of a sensor.
The object can be achieved by a capacitance type displacement detection apparatus, according to the present invention, comprising:
a detection portion having a transmission electrode and a detection electrode formed thereon which are capacitance-coupled to a reception electrode formed on an opposite scale; and
a signal processing portion which supplies a driving signal to the transmission electrode of the detection portion and receives a detection signal from the detection electrode.
In the apparatus, both the detection portion and the signal processing portion are formed on a board made of silica glass, glass, quartz, ceramic or alumina.
It is preferable that the detection portion is formed on one surface of the board and the signal processing portion is formed on the other surface of the board. Incidentally, the board may be made of composite material of silica glass, glass, quartz, ceramic and alumina.
The object can be also achieved by a method of manufacturing a capacitance type displacement detection apparatus, which includes
a detection portion having a transmission electrode and a detection electrode formed thereon which are capacitance-coupled to a reception electrode formed on an opposite scale; and
a signal processing portion which supplies a driving signal to the transmission electrode of the detection portion and receives a detection signal from the detection electrode. The method comprises the steps of:
sequentially forming a conductive layer and a coupling layer on a board made of silica glass, glass, quartz, ceramic or alumina; and
forming the detection portion on the conductive layer and forming the signal processing portion on the coupling layer to thereby form both the detection portion and the signal processing portion on the board.
Further, the object can be achieved by a method of manufacturing a capacitance type displacement detection apparatus, which includes
a detection portion having a plurality of transmission electrodes and a plurality of detection electrodes formed thereon which are capacitance-coupled to a reception electrode formed on an opposite scale; and
a signal processing portion which supplies a driving signal to the transmission electrodes of the detection portion and receives a detection signal from the detection electrodes. The method comprises the steps of:
forming a conductive layer on each of both surfaces of a board made of silica glass, glass, quartz, ceramic or alumina;
forming a coupling layer on at least one of the both surfaces of the board; and
forming the detection portion on one of the both surfaces of the board and forming the signal processing portion on the coupling layer on other of the both surfaces of the board. In this respect, it is preferable that the coupling layer is made of palladium, solder or nickel. Further, it is preferable that at least part of the signal processing portion is formed on the coupling layer by flip chip, BGA (Ball Grid Array) or CSP (Chip Size Package).
According to the invention, unlike the related art technique, the detection portion and the signal processing portion are not formed on the different boards but commonly formed on a board made of silica glass, glass, quartz, ceramic or alumina. Thus, the distance between the detection portion and the signal processing portion can be shortened and the distance required for drawing the wirings can be shortened and so the noise mixing can be effectively suppressed. Further, when the signal processing portion is formed on a substrate made of quartz, glass or ceramic, the design rule can be reduced (more fine processing becomes possible) as compared with a case of forming on a resinboard made of epoxy resin etc., for example, the entire size of the sensor can also be miniaturized.
As modes of forming both the detection portion and the signal processing portion on the same board, there area mode of forming these portions on one surface of the board and another mode of respectively forming these portions on both surfaces of the board. In the mode of respectively forming these portions on both surfaces of the board, since the detection portion is formed on one surface of the board and the signal processing portion is formed on the other surface of the board, the board can be used effectively and also the size of the board itself can be reduced. In the case of forming both the signal processing portion and the detection portion on the same board, it is preferable to employ the flip chip, BGA or CSP since the coupling area can be miniaturized. Further, when the coupling layer is formed on the conductive layer on the board, the contact property can be improved and so the signal processing portion can be formed surely.